JP7061828B2 - Waterproof sound-permeable membrane and waterproof sound-permeable structure using it - Google Patents

Description

The present invention relates to a waterproof sound-permeable membrane and a waterproof sound-transmitting structure using the same.

In electronic devices such as mobile phones, smartphones, and digital video cameras, an audio device is housed in a housing. These enclosures have openings to allow the passage of audio. In order to prevent water from entering the housing, a waterproof sound-transmitting film that allows the passage of sound while blocking the passage of sound is attached to this opening. As the waterproof sound-transmitting membrane, a polytetrafluoroethylene (PTFE) porous membrane is often used.

Patent Document 1 discloses a waterproof sound-transmitting membrane having both low acoustic transmission loss and high water pressure resistance. According to Patent Document 1, the important parameters to be focused on are the mass and thickness of the waterproof sound-permeable membrane, not the air permeability (air flow through the membrane). Decreasing both mass and thickness increases the sound energy propagated by the vibration of the waterproof sound-permeable membrane. Therefore, even if the air permeability is lowered in order to realize high water pressure resistance, the acoustic transmission loss does not increase. In Patent Document 1, the thickness of the waterproof sound-transmitting membrane is 3 to 33 μm, the mass is 40 g / m ² or less, and the air permeability indicated by the Garley number is 1 second or more (displayed by the Frazier number, about 1. 57 cm ³ / cm ² / s or less) is disclosed.

Japanese Unexamined Patent Publication No. 2011-142680

The sound-transmitting characteristics of the waterproof sound-transmitting membrane were evaluated using the acoustic transmission loss as an index. However, the quality of the propagating sound, specifically the degree of so-called vowel breaking, is also an important characteristic in practical use. On the other hand, the degree of waterproof characteristics required for a waterproof sound-permeable membrane varies depending on the type and application of the electronic device. For example, it is not necessary to consider the use in water, but electronic devices that are only supposed to come into contact with water droplets such as rainwater do not require a high water pressure resistance of 100 kPa or more, and are of the so-called water resistant level. It suffices if a waterproof sound-transmitting film capable of achieving water pressure resistance is provided.

An object of the present invention is to provide a waterproof sound-transmitting film suitable for waterproofing at a level of daily life waterproofing or higher and suppressing the occurrence of sound cracking.

According to the study by the present inventors, it is necessary to adjust the air permeability of the waterproof sound-transmitting membrane in order to suppress the occurrence of sound cracking.

The present invention
It has a sound-transmitting region containing a PTFE porous membrane and has a sound-transmitting region.
The air permeability in the thickness direction of the porous membrane measured in accordance with the A method (Frazier method) of the air permeability measurement method specified in JIS L1096 is 2 cm ³ / cm ² / s or more.
Provided is a waterproof sound-permeable membrane having a water pressure resistance of 3 kPa or more measured in accordance with the waterproof test method B (high water pressure method) specified in JIS L1092.

Further, the present invention
A housing with an opening and
Provided is a waterproof sound-transmitting structure comprising the waterproof sound-transmitting membrane of the present invention attached to the housing so as to close the opening.

According to the present invention, the water pressure resistance of the PTFE porous membrane is 3 kPa or more, and the air permeability indicated by the number of Fraziers of the PTFE porous membrane is 2 cm ³ / cm ² / s or more (expressed by the number of Garley, about. Since it is 0.79 seconds or less), it is possible to provide a waterproof sound-transmitting film suitable for waterproofing of daily life waterproof level or higher and suppression of occurrence of sound cracking.

It is sectional drawing which shows typically the example of the waterproof sound-transmitting membrane of this invention. It is a perspective view schematically showing an example of the waterproof sound-transmitting membrane of this invention. It is an enlarged sectional view schematically showing an example of the waterproof sound-transmitting structure of this invention. It is an enlarged sectional view schematically showing an example of the electronic device to which the waterproof sound-transmitting film of this invention was applied. It is a schematic diagram for demonstrating the evaluation method of the waterproof sound-transmitting membrane used in an Example. It is a graph which shows the relationship between the air permeability and the sound distortion in an Example and a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of the waterproof sound-transmitting film 10 of the present embodiment, and FIG. 2 is a perspective view of the waterproof sound-transmitting film 10. The waterproof sound-transmitting membrane 10 has a sound-transmitting region 13c that allows the passage of sound, and a peripheral region 13p that surrounds the sound-transmitting region 13c. The sound transmission region 13c is composed of a single-layer PTFE porous membrane 11. The peripheral region 13p includes a PTFE porous membrane 11 and an adhesive layer 12. The adhesive layer 12 may be composed of only the adhesive, but may be a double-sided tape.

The air permeability of the PTFE porous membrane 11 in the thickness direction is 2 cm ³ / cm ² / s or more in terms of the value given by the A method (Frazil method) of the air permeability measurement method specified in JIS L1096. The air permeability of the PTFE porous membrane 11 in the thickness direction is preferably 3 cm ³ / cm ² / s or more, and more preferably 5 cm ³ / cm ² / s or more. In the waterproof sound-transmitting membrane 10 of the present embodiment, since the range of air permeability of the PTFE porous membrane 11 is adjusted as described above, the occurrence of sound cracking can be suppressed. The air permeability of the PTFE porous membrane 11 in the thickness direction is preferably 25 cm ³ / cm ² / s or less, and more preferably 6 cm ³ / cm ² / s or less.

The water pressure resistance of the PTFE porous membrane 11 is 3 kPa or more in terms of the value given by the B method (high water pressure method) of the waterproof test method specified in JIS L1092. Since the water pressure resistance of the PTFE porous membrane 11 is 3 kPa or more, the waterproof property of at least the protection class against water intrusion specified in JIS C0920 is 4th grade (IPX4, protection class equivalent to the daily life waterproof level) or higher. can. The water pressure resistance of the PTFE porous membrane 11 is preferably 15 kPa or more and 75 kPa or less, and more preferably 20 kPa or more and 50 kPa or less.

From the viewpoint of further enhancing waterproofness while sufficiently suppressing the occurrence of sound cracking, the PTFE porous membrane 11 has a breathability of 5 cm ³ / cm ² / s or more and a water pressure resistance of 20 kPa or more and 50 kPa or less. Is particularly preferred.

The mass of the PTFE porous membrane 11 is, for example, 4 g / m ² or less. The mass of the PTFE porous membrane 11 is preferably 2 g / m ² or less, and more preferably 1.5 g / m ² or less. The thickness of the PTFE porous membrane 11 is, for example, 17 μm or less. The thickness of the PTFE porous membrane 11 is preferably 15 μm or less, more preferably 11 μm or less.

The waterproof sound-transmitting membrane 10 of the present embodiment includes a double-sided tape as an adhesive layer 12 for adhering the PTFE porous membrane 11 to a mating material (housing or the like). The double-sided tape is attached to the surface 11f of the peripheral edge portion 11p of the PTFE porous membrane 11. The adhesive layer 12 such as double-sided tape is arranged on the surface 11f of the PTFE porous membrane 11 so as to surround the sound-transmitting region 13c. The adhesive layer 12 may be formed on the back surface 11b, or may be formed on both the front surface 11f and the back surface 11b.

The PTFE porous membrane 11 may be subjected to a water-repellent treatment or an oil-repellent treatment. The water-repellent treatment or the oil-repellent treatment can be carried out, for example, by impregnating the PTFE porous membrane 11 with a material having a surface tension lower than that of PTFE from the front surface 11f and / or the back surface 11b.

The PTFE porous film 11 may contain a colorant such as a pigment or a dye. Examples of the dye include azo dyes and oil-soluble dyes. An example of a preferred colorant is carbon black.

FIG. 3 shows a waterproof sound-transmitting structure 20 in which the waterproof sound-transmitting membrane 10 is arranged. The waterproof sound-transmitting structure 20 includes a housing 21 having an opening 22 and a waterproof sound-transmitting membrane 10 attached to the housing 21 so as to close the opening 22. The waterproof sound-transmitting film 10 is fixed to the housing 21 by the adhesive force of the adhesive layer 12. It is also possible to omit the adhesive layer 12 and directly fix the PTFE porous membrane 11 to the housing 21 by ultrasonic bonding or the like. In this case, the waterproof sound-transmitting membrane 10 is composed of a single-layer PTFE porous membrane 11 even in the peripheral region 13p.

FIG. 4 shows a mobile phone 30 as an example of an electronic device to which a waterproof sound-transmitting membrane 110 provided with a PTFE porous membrane 11 is applied. The waterproof sound-transmitting film 110 in the mobile phone 30 is the same as the waterproof sound-transmitting film 10 except that a double-sided tape is also attached to the back surface 11b of the PTFE porous film 11 as an adhesive layer 12. ..

The microphone 33 is housed in the housing 38 of the mobile phone 30. The housing 38 is provided with a first sound collecting port 39 that guides sound from the outside to the microphone 33. A sound collecting unit 34 that converts voice into an electric signal is housed in the package 35 of the microphone 33. One surface of the package 35 is provided with a second sound collecting port 36 that guides the sound introduced from the first sound collecting port 39 of the housing 38 to the sound collecting unit 34 of the microphone 33. The first sound collecting port 39 and the second sound collecting port 36 are separated by a waterproof sound transmitting film 110. The microphone 33 is electrically connected to the circuit board 31 of the mobile phone 30 by a terminal (not shown) provided on the bottom surface of the package 35, and the electric signal converted from the sound by the sound collecting unit 34 is generated. It is output to the circuit board 31 via the terminals. In the mobile phone 30, the microphone 33 is collected from the first sound collecting port 39 and the second sound collecting port 36 by the waterproof sound collecting film 110 arranged so as to block the first sound collecting port 39 and the second sound collecting port 36. Sound can be passed through the sound collecting unit 34 while preventing foreign matter such as dust and water from entering the sound unit 34.

Next, an example of a manufacturing method suitable for manufacturing a waterproof sound-transmitting membrane made of a PTFE porous membrane having a single-layer sound-passing region as described above will be described.

First, a mixture containing PTFE fine powder and a processing aid (liquid lubricant) in a predetermined ratio is sufficiently kneaded to prepare a paste for extrusion molding. Next, the preformed paste is molded by a known extrusion method to obtain a sheet-shaped or rod-shaped molded product. Next, the sheet-shaped or rod-shaped molded body is rolled to obtain a strip-shaped PTFE sheet. Next, the rolled PTFE sheet is dried in a dryer. The processing aid is volatilized by the drying step, and a PTFE sheet in which the content of the processing aid is sufficiently reduced can be obtained. Next, the dried PTFE sheet is stretched in the longitudinal direction (MD) and in the width direction (TD) orthogonal to the longitudinal direction, respectively. The PTFE sheet stretched in the biaxial direction may be fired at a temperature equal to or higher than the melting point of PTFE.

From the viewpoint of producing a waterproof sound-transmitting film with small sound distortion, the PTFE sheet is stretched at a temperature equal to or lower than the melting point of PTFE (for example, 327 ° C.), and then the PTFE sheet is thermally fixed at a temperature equal to or higher than the melting point of PTFE. Is preferable. The temperature at which the PTFE sheet is stretched is, for example, 50 ° C to 320 ° C, preferably 100 ° C to 300 ° C. The temperature at the time of heat fixing is, for example, 330 ° C. to 400 ° C., preferably 350 ° C. to 380 ° C.

(Example 1)
20 parts by weight of a liquid lubricant (n-dodecane, manufactured by Japan Energy Co., Ltd.) was uniformly mixed with 100 parts by weight of PTFE fine powder (F104, manufactured by Daikin Industries, Ltd.). The resulting mixture was compressed in a cylinder and then ram extruded to give a sheet. The obtained sheet was passed between metal rolling rolls in a state containing a liquid lubricant, compressed to a thickness of 0.2 mm, and dried by heating at 150 ° C. to remove the liquid lubricant. As a result, an unfired sheet-shaped molded product was obtained. This sheet-shaped molded product was stretched at 300 ° C. in the longitudinal direction at a magnification of 10 times, and then at 100 ° C. at a magnification of 30 times in the width direction. Then, the sheet-shaped molded product was allowed to stand at 360 ° C., which is higher than the melting point of PTFE, and heat-fixed. In this way, the PTFE porous membrane of Example 1 was obtained.

(Example 2)
A PTFE porous membrane of Example 2 was obtained by the same procedure as in Example 1 except that it was stretched at a magnification of 20 times in the longitudinal direction and stretched at a magnification of 40 times in the width direction.

(Example 3)
A PTFE porous membrane of Example 3 was obtained by the same procedure as in Example 1 except that it was stretched at a magnification of 25 times in the longitudinal direction and stretched at a magnification of 40 times in the width direction.

(Example 4)
A PTFE porous membrane of Example 4 was obtained by the same procedure as in Example 1 except that it was stretched at a magnification of 30 times in the longitudinal direction and stretched at a magnification of 40 times in the width direction.

(Comparative Example 1)
A PTFE porous membrane of Comparative Example 1 was obtained by the same procedure as in Example 1 except that it was stretched at a magnification of 3 times in the longitudinal direction and stretched at a magnification of 40 times in the width direction.

(Comparative Example 2)
A PTFE porous membrane of Comparative Example 2 was obtained by the same procedure as in Example 1 except that it was stretched at a magnification of 5 times in the longitudinal direction and stretched at a magnification of 50 times in the width direction.

(Comparative Example 3)
A PTFE porous membrane of Comparative Example 3 was obtained by the same procedure as in Example 1 except that it was stretched at a magnification of 8 times in the longitudinal direction and stretched at a magnification of 10 times in the width direction.

(Comparative Example 4)
A non-porous polyethylene terephthalate (PET) film (Lumilar (registered trademark) F53, manufactured by Toray Industries, Inc.) was prepared.

The thickness, weight, air permeability, water pressure resistance, sound distortion, sound loss and sound cracking of the PTFE porous membranes of Examples 1 to 4 and Comparative Examples 1 to 3 and the PET film of Comparative Example 4 are as follows. I checked the degree of.

[thickness]
The thickness of the PTFE porous film and the PET film was measured using a dial gauge having a mesh size of 0.001 mm and a stylus outer diameter of 10 mm.

[weight]
The weight of the PTFE porous membrane and the PET film was determined by cutting out the PTFE porous membrane and the PET film in a 10 cm square, measuring the weight, and then determining the weight per unit area.

[Draft]
The air permeability of the PTFE porous membrane and PET film is based on the A method (Frazil method) specified in JIS L1096, and the number of Frazier (per unit area and unit time when a predetermined pressure is applied). It was determined by the amount of air passing through the PTFE porous film and the PET film).

[Water pressure resistance]
The water pressure resistance of the PTFE porous membrane was determined by using a water resistance test device (for high water pressure) in accordance with the waterproof test method B method (high water pressure method) specified in JIS L1092. However, since the membrane is significantly deformed in the area specified in JIS L1092, a stainless mesh (opening diameter 2 mm) was installed on the opposite side of the pressure surface of the membrane, and the measurement was performed with the deformation suppressed.

[Sound distortion]
The sound distortion in the sample was evaluated as follows.

First, as shown in FIG. 5, a simulated housing 41 (made of acrylic, length 70 mm × width 50 mm × height 15 mm) imitating a mobile phone housing was prepared. The simulated housing 41 is composed of a first portion 41a and a second portion 41b, and the first portion 41a and the second portion 41b can be fitted to each other. The first portion 41a is provided with a mounting hole 42 (diameter 13 mm). By fitting the first portion 41a and the second portion 41b to each other, a space having no openings other than the mounting hole 42 and the conduction port 43 of the lead wire 44 is formed in the simulated housing 41.

Separately, the PTFE porous membrane and PET film prepared in each Example and Comparative Example (in FIG. 5, the PTFE porous membrane is designated by reference numeral 211) are circular with a diameter of 16 mm using a Thomson type. Punched out. Next, a ring-shaped double-sided tape 212 having an outer diameter of 16 mm and an inner diameter of 13 mm was attached to the peripheral edges of both main surfaces of the punched PTFE porous membrane. Then, the PTFE porous film was attached to the speaker 45 (manufactured by Star Micronics, SCC-16A, diameter 16 mm) as a sound source via one double-sided tape 212.

Next, the speaker 45 to which the PTFE porous membrane is attached faces the mounting hole 42 in the first portion 41a of the simulated housing 41, the PTFE porous membrane faces the mounting hole 42, and the PTFE porous membrane faces the mounting hole 42. Was fixed from the inner surface when fitted with the second portion 41b so as to close the surface. The speaker 45 is fixed to the first portion 41a by the double-sided tape 212 attached to the surface of the PTFE porous membrane opposite to the speaker 45 side, and at that time, the double-sided tape 212 does not cover the mounting hole 42. At the same time, care was taken to ensure that the mounting hole 42 was completely closed by the PTFE porous membrane.

Next, while guiding the lead wire 44 of the speaker 45 to the outside of the simulated housing 41 through the conduction port 43, the first portion 41a and the second portion 41b are fitted together, and the sound loss of the PTFE porous membrane is measured. A simulated housing 41 for the purpose was formed. The conduction port 43 was closed with putty after the lead wire 44 was led out.

Next, the lead wire 44 and the microphone (combination of Type 2669 and Type 4192 manufactured by B & K) were connected to a sound transmissibility evaluation device (3560-B-030 manufactured by B & K), and were separated from the speaker 45 by 50 mm. I placed a microphone in the position.

Harmonic distortion (THD) was evaluated as sound distortion with the PTFE porous membrane installed as described above. Harmonic distortion was determined by the ratio (%) of the measured values of all harmonics to the measured values of the fundamental wave. The measured values of all harmonics are the measured values of the second harmonic and the third harmonic.

[Sound loss]
The sound loss in the sample was evaluated as follows by preparing an evaluation device similar to the above-mentioned sound distortion evaluation device.

As described above, the volume received by the microphone with the PTFE porous membrane installed and the volume received by the microphone in the same state except that the PTFE porous membrane was omitted were measured, and from these differences. Sound loss (dB) was evaluated. The frequency of the sound used for the measurement was 1000 Hz. If the loss is 5 dB or less, it can be said that the sound permeability is high.

[Vowel breaking]
The degree of sound cracking in the sample was evaluated as follows by preparing an evaluation device similar to the above-mentioned sound distortion evaluation device.

With the PTFE porous membrane installed as described above, it was evaluated by a sensory test whether or not the sound heard by the ear was cracked. When the sound heard by the ear is not cracked, it is judged that there is no cracking (○), and when the sound heard by the ear is slightly cracked, it is judged that there is a slight cracking (△), and it is judged by the ear. When the heard sound was cracked, it was determined that the sound was cracked (x).

Table 1 shows the results of evaluating the thickness, weight, air permeability, water pressure resistance, sound distortion, sound pressure loss, and degree of sound cracking of the PTFE porous film and PET film as described above.

In Examples 1 to 4, it was determined that the sound distortion and sound loss were small and there was no sound cracking (◯). Therefore, it can be said that the PTFE porous membranes of Examples 1 to 4 were able to suppress the occurrence of sound cracking as compared with the conventional PTFE porous membrane while reducing the sound loss when passing through the PTFE porous membrane.

The reason why the sound distortion and the sound loss were small in Examples 1 to 4 is that the present inventors have ventilated the PTFE porous membrane so that the air permeability of the PTFE porous membrane is 2 cm ³ / cm ² / s or more. It is presumed that this is because it is formed so as to have a high degree. As shown in FIG. 6, when the air permeability indicated by the number of Frazier is in the range of 0 to 2 cm ³ / cm ² / s, the sound distortion sharply decreases as the air permeability increases. On the other hand, in the range of air permeability of 2 cm ³ / cm ² / s or more, the decrease of sound distortion becomes gradual. It can be confirmed that the air permeability should be adjusted to 2 cm ³ / cm ² / s or more in order to eliminate the sound distortion caused by the vibration of the membrane.

Further, in Examples 1 to 4, since the water pressure resistance of the PTFE porous membrane is in the range of 3 kPa or more, it is possible to secure the waterproofness of the PTFE porous membrane of IPX4 or higher, which is a protection grade corresponding to at least the life waterproof level. Therefore, the PTFE porous membranes of Examples 1 to 4 can impart sufficient waterproofness to electronic devices used in daily living environments. Therefore, the PTFE porous membranes of Examples 1 to 4 can be suitably used for electronic devices in which acoustic characteristics are more important.

The waterproof sound-transmitting membrane of the present invention can be suitably used for an electronic device in which an audio device is housed. Specifically, it can be suitably used for mobile phones, smartphones, digital video cameras and the like.

10,110 Waterproof sound-transmitting film 11,211 PTFE porous film 11b Back surface 11f Surface 11p Peripheral part 12 Adhesive layer 13c Sound-transmitting area 13p Peripheral area 20 Waterproof sound-transmitting structure 21 Housing 22 Opening 30 Mobile phone 31 Circuit board 33 Microphone 34 Sound collecting part 35 Package 36 2nd sound collecting port 38 Housing 39 1st sound collecting port 41 Simulated housing 41a 1st part 41b 2nd part 42 Mounting hole 43 Conduction port 44 Lead wire 45 Speaker 212 Double-sided tape

Claims (5)

It has a sound-transmitting region containing a polytetrafluoroethylene porous membrane and has a sound-transmitting region.
The air permeability in the thickness direction of the porous membrane measured in accordance with the A method (Frazier method) of the air permeability measurement method specified in JIS L1096 is 2 cm ³ / cm ² / s or more and 20 cm ³ / cm ² /. Less than s
Harmonic distortion is 70% or less,
The water pressure resistance of the polytetrafluoroethylene porous membrane measured in accordance with the waterproof test method B (high water pressure method) specified in JIS L1092 is 50 kPa or less.
The sound-transmitting region is composed of only a single layer of the polytetrafluoroethylene porous membrane.
Waterproof sound-permeable membrane. The waterproof sound-transmitting membrane according to claim 1, wherein the sound loss for a sound having a frequency of 1000 Hz is 1.0 dB or less. The waterproof sound-transmitting membrane according to claim 1 or 2, wherein the air permeability is 6 cm ³ / cm ² / s or less. The waterproof sound-transmitting membrane according to any one of claims 1 to 3 , wherein the water pressure resistance of the polytetrafluoroethylene porous membrane is 3 kPa or more. A housing with an opening and
A waterproof sound-transmitting structure comprising the waterproof sound-transmitting membrane according to any one of claims 1 to 4 , which is attached to the housing so as to close the opening.

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